1. [4pts] Write down a formula for the equation of the tangent plane to the graph of a function, z = f(x, y), at the point (x0, y0).

2. [3pts] Suppose that z = f(x, y) is a function and (x, y) = r(t) is a curve in the plane. Write down a version of the chain rule that you can use to calculate z 0 (t).

3. [3pts] State a formula for the directional derivative of z = f(x, y) at a point x0 = (x0, y0) in the direction of the vector u = (a, b). Your answer should involve the gradient of f.